In recent years, a touch panel system, which accepts a user's instruction by detecting a position of an indicator (e.g., a user's finger or a stylus, hereinafter) that is in contact with or close to a detection surface of a touch panel, has been increasingly installed in a cell phone, a personal computer, a vending machine, and the like. Further, recently, a projection type capacitive touch panel system in which a multi-touch operation (simultaneously detecting a plurality of indicators in contact with or close to the detection surface of the touch panel) has come to be broadly used in place of a resistive film touch panel system.
In the projection type capacitive touch panel system, there is used a touch panel including a plurality of upper electrodes that are provided so as to be parallel to each other along the detection surface, and lower electrodes that are provided so as to intersect with the upper electrodes and to be parallel to each other along the detection surface. In this touch panel, the upper electrode is provided between the lower electrode and the detection surface, and the upper electrode and the lower electrode form a two-layer structure.
The projection type capacitive touch panel system has a self-capacitive system and a mutual capacitive system. The self-capacitive system acquires a signal from each of the upper electrode and the lower electrode to detect a change (increase) in capacitance of each of the upper electrode and the lower electrode, to separately detect a position of the indicator in an array direction of the upper electrodes and a position of the indicator in an array direction of the lower electrodes. On the other hand, the mutual capacitive system drives one electrode (hereinafter, the case of the lower electrode will be illustrated) and acquires a signal from the other electrode (hereinafter, the case of the upper electrode will be illustrated), to detect a change (decrease) in capacitance between the upper electrode and the lower electrode, thereby detecting a position of the indicator within the detection surface.
In the projection type capacitive touch panel system, a distance between the detection surface and the lower electrode is longer than a distance between the detection surface and the upper electrode. For this reason, in the self-capacitive touch panel system, at a time when the indicator comes into contact with or close to the detection surface, an amount of change (amount of increase) in capacitance of the lower electrode becomes smaller than an amount of change (amount of increase) in capacitance of the upper electrode. Therefore, the detection accuracy of the position of the indicator based on the output signal of the lower electrode becomes lower than the detection accuracy of the position of the indicator based on the output signal of the upper electrode.
Therefore, Patent Document 1 proposes a self-capacitive touch panel system in which an area of the lower electrode is made larger than an area of the upper electrode, to make larger the amount of change (amount of increase) in capacitance of the lower electrode at a time when the indicator comes into contact with or close to the detection surface.